Our goal is to design and establish novel therapeutic agents for sickle cell disease (SCD), namely drugs that inhibit the initial sickle hemoglobin (HbS) polymerization and the subsequent pathophysiology. When deoxygenated, HbS polymerizes into long, rigid, and insoluble fibers causing red blood cells (RBCs) to sickle, a process worsened by the unusual low affinity of HbS for oxygen, resulting in premature release of oxygen. Based on several evidence--our preliminary data, studies by others, and the results of a recently completed phase I/II clinical testing of our lead compound, 5-HMF (an allosteric effector of Hb, AEH)-we hypothesize that AEHs, not only prevent HbS polymerization, but also mitigates several secondary sickling related pathological events that include inflammation, oxidative stress/damage, RBC hemolysis, and pain. We also have preliminary evidence that our next generation AEHs (INN- and TD-series) exhibit enhanced potency and improved in-vitro duration of action. These AEHs act via a novel mechanism of action, i.e., destabilize HbS polymer contacts, in addition to increasing Hb affinity for oxygen; providing positive synergistic effects. We propose to test our hypothesis by further investigating candidate drugs from the INN- and TD-series, as well as derivatives of 5-HMF and INN-312 for their pharmacologic properties, focusing on the secondary SCD pathways, as well as the underlying HbS polymerization problem using our model systems. The specific aims are: 1. Design and synthesis of novel allosteric effectors of hemoglobin (AEHs). We will modify our parent compounds and synthesize derivatives with enhanced efficacy and prolonged half-lives. We will also synthesize prod rugs to protect the active aldehyde functional moiety from aldehyde dehydrogenase (ALDH)- mediated metabolism as necessary. 2. Investigate in-vitro functional, ant sickling, and cytotoxicity activities of novel AEHs. We will investigate the AEHs for their in-vitro ant sickling/functional activities (RBC sickling tests, P50 analyses, HbS solubility, and Hb adduct formation), and carefully monitor for adverse effects. 3. Determine in-vivo/in-vitro PK/PD properties, binding and metabolism and evaluate preclinical efficacy of AEHs in SCD Berkeley mice. We will show that serum albumin binding and/or metabolism by ALDH in RBC or hepatic cytosol are not likely to adversely affect in-vivo pharmacologic activity. We will demonstrate using a Berkeley mouse model of SCD transgenic mice that AEHs show potent pharmacologic effects, increase short- and long-term survival rates of mice. We will also study their potential beneficial effects, e.g. amelioration of hemolysis, inflammation, endothelial damage, and overall reversal of the SCD pathophysiology observed in this model. 4. Determine the atomic interactions between AEHs and Hb. X-ray crystallography will be used to validate our hypothesis that AEH potency is directly dependent upon their abilities to bind Hb with their pyridyl substituents toward the surface of the Hb molecule. The structures would provide valuable insight to help guide rational modifications for better pharmacologic properties.